Fish Microbiology and Quality Assurance

10. Sugar fermentation test

This test is carried to determine the ability of microorganisms to utilize different carbohydrate as carbon source with resultant production of acid and gas. The bromothymol blue indicator used in the medium indicates acidic pH due to sugar fermentation by change in colour from purple to yellow.

Procedure:
To the test tubes containing different sugars and Durham’s tube to collect gas are inoculated with test cultures and incubated at 37⁰c for 24 hours. The change in colour from purple is yellow is indicative of positive result.

Sugar fermentation medium

Soya peptone : 1.0 g
Sodium chloride : 1.0 g
Sugars : 1.0 g
Bromocresol purple : 0.0016%
Distilled water : 100 ml
pH : 7.2 ± 0.2

The media containing individual sugars dissolved and dispensed in 4 ml volumes in test tubes containing inverted Durham’s tube and autoclaved at 11⁰c for 10 minutes.